If I had to venture a guess, under the assumption that there is intelligent life out there...

My guess is that Interstellar trade, conflict, and communications aren't worth the trip. Massive amounts of time and resources go into sending an envoy to another planet, and for what? Foodstuffs that aren't compatible with our physiology? Finished goods, information, and technology that are designed for a physiology and culture entirely alien to ours? Resources that can be sourced in abundance from worlds that are either uninhabited or inhabited solely by non-sentient creatures?

There is value for us in interacting with tribal societies because we have some fundamental things in common with them, both being human. There can be value in some of there local medicine, foods, and other traditions, as well as insights into our own development- but it's rare, even with those similarities, for a tribal society to produce a finished good that ends up in demand. Make it another species, and the few benefits here might be gone. And when we're attempting to learn from them by observation, it's often in our best interest to remain undetected while doing so- both for our own protection and to avoid influencing the society and coloring our own results.

The calculations that predict the number of civilizations there 'should' be all seem to be making a lot of assumptions as well.

So, my explanations are as follows:

The calculation is probably wrong.

Visiting or contacting earth represents a significant cost in time, materials, and energy.

Few evident gains to justify said expenditures.

What gains I can conceive of would directly benefit from the other intelligent society remaining 'invisible.'

WHY no one has come to visit might simply be there are hundreds of billions of places to go that are more interesting than our unimaginablely small little third rock from the sun.